1. Field of the Invention
The present invention relates to a digital image coding apparatus using watermarking, a decoding apparatus, and coding and decoding methods, and more particularly, to a digital image encoding apparatus for inserting an original signature image into a significant area of a host image during encoding, evaluating variance between the host image and the original signature image during decoding, thereby precisely estimating the quality of the host image, a corresponding decoding apparatus, and corresponding encoding and decoding methods.
2. Description of the Related Art
Watermarking is a technology in which an image to be transmitted is transmitted together with an encrypted image for the purpose of providing security and authentication rights. A receiver side receives the image to be transmitted (hereinafter to be referred to as a host image) together with the encryption image transmitted with confidence (hereinafter to be referred to as a signature image). The signature image is decoded by a special decryption apparatus.
FIG. 1 is a conceptual block diagram illustrating a conventional digital image codec apparatus 1 for generating a watermarked image 8 and extracting a signature image 14 from the watermarked image. In the conventional digital image codec apparatus, during encoding, a DCT (Discrete Cosine Transform) 2 is performed on a host image 3 and a secret signature image 4 to be transmitted, thereby extracting DCT coefficients for the respective images. The DCT coefficients are encoded by an encoder 5. Here, the DCT coefficient components of the signature image 4 are encoded by a separate encryption encoder 6 that controls the encryption operation. In such a manner, the DCT coefficients of the host image 3 and the DCT coefficients of the signature image 4 inserted into the DCT coefficients of the host image 3 after being encoded, can be transmitted. An IDCT (Inverse Discrete Cosine Transform) 7 is performed on the DCT coefficients 2A of the host image and the DCT coefficients 2B of the signature image inserted into the DCT coefficients of the host image, thereby obtaining a watermarked image 8 in which only the host image is visible, while the signature image is not visible.
The signature image 4 watermarked on the host image 3 is decoded by a special decryption apparatus to then be restored. During restoration, IDCT is performed on a watermarked image, thereby extracting DCT coefficients thereof. Next, the extracted DCT coefficients 2A obtained by performing DCT on the original host image 3, are separated from the DCT coefficients of the watermarked image at subtractor 10, thereby extracting DCT coefficient components of the encoded signature image. Then, a decoder 11 decodes the DCT coefficient components of the encoded signature image. Here, the encryption decoder 11 performs a control operation for the decryption process. The DCT coefficients of the signature image decoded by the decryption control operation are again IDCT-performed 13, thereby restoring the signature image.
As described above, in the conventional digital image codec apparatus using watermarking, a conventional method for evaluating the quality of a transmitted image is performed by comparing the transmitted current image with the previous image in various ways. The conventional method is based on the assumption that the current image is not significantly different from the previous image. However, this assumption is not applied to an abruptly changing image screen. In this case, image evaluation is not accurately performed. Also, even if the assumption is proper, the image evaluation is less correct than in the case of a comparison with the original image.
It is a first object of the present invention to provide a digital image coding apparatus which can precisely estimate the quality of a host image by transmitting a small quantity of image samples, which are suitable for the application of an analysis of variance (ANOVA) technique, as a signature image using watermarking during encoding without affecting an original image, and by performing an ANOVA technique on the restored signature image and the original signature image during decoding.
To achieve the above object of the present invention, there is provided a digital image coding apparatus for recording a signature image on a host image using watermarking, including a first discrete wavelet transform portion for receiving a host image to be transmitted and performing discrete wavelet transform thereon, thereby outputting Mxc3x97M discrete wavelet coefficients where M is a predetermined positive integer, an original signature image storage portion for storing an image, which is suitable to the performance of an analysis-of-variance (ANOVA) technique as an original signature image, a second discrete wavelet transform portion for receiving the original signature image and performing discrete wavelet transform thereon to obtain Nxc3x97N wavelet coefficients, N being another predetermined integer smaller than M, and a coefficient replacement/combination portion for replacing and combining Nxc3x97N location data with Nxc3x97N wavelet coefficients selected among Mxc3x97M wavelet coefficients in accordance with a predetermined rule to then output the Nxc3x97N location data and replaced Mxc3x97M wavelet coefficients.
Also, the digital image coding apparatus may further include an inverse discrete wavelet transform portion for performing inverse discrete wavelet transform on the replaced Mxc3x97M wavelet coefficients to generate a combined host image.
Also, the digital image coding apparatus may further include a compression portion for compressing the combined host image and the Nxc3x97N location data.
The predetermined positive integer N is preferably smaller than or equal to xe2x85x9 of the predetermined positive integer M.
Also, the predetermined rule preferably is to select 50% of the upper significant wavelet coefficients among Mxc3x97M wavelet coefficients.
According to another aspect of the present invention, there is provided a digital image decoding apparatus for receiving bitstreams having a signature image recorded on a host image using watermarking and for restoring the host image and the signature image, including a coefficient separating portion for separating Nxc3x97N wavelet coefficients from the Mxc3x97M wavelet coefficients using the Nxc3x97N location data, M being a predetermined positive integer and N being another predetermined integer smaller than M, an inverse discrete wavelet transform portion for performing inverse discrete wavelet transform on the Nxc3x97N wavelet coefficients to generate a restored signature image, an original signature image storage portion for storing the signature image, which is suitable to the performance of an ANOVA technique and which is the same as that used in watermarking of the host image as the original signature image, and an ANOVA portion for applying the original signature image and the restored signature image to an ANOVA technique to output variance characteristic data of the restored signature image as image quality indication data.
Also, the digital image decoding apparatus may further include a decompression portion for receiving the bitstreams having the combined host image and the Nxc3x97N location data compressed therein, and decompressing the same to output the combined host image, and Nxc3x97N location data representing the locations of signature image discrete wavelet coefficients, and a discrete wavelet transform portion for performing discrete wavelet transform on the combined host image to obtain Mxc3x97M wavelet coefficients, M being a predetermined positive integer.
According to another aspect of the present invention, there is provided a digital image codec apparatus for recording a signature image on a host image using watermarking, and restoring the host image and the signature image, including: a first discrete wavelet transform portion for receiving a host image to be transmitted and performing discrete wavelet transform thereon, thereby outputting Mxc3x97M discrete wavelet coefficients where M is a predetermined positive integer, a first original signature image storage portion for storing an image, which is suitable to the performance of an analysis of variance (ANOVA) technique, as an original signal image, a second discrete wavelet transform portion for receiving the original signature image and performing discrete wavelet transform thereon to obtain Nxc3x97N wavelet coefficients, N being another predetermined integer smaller than M, a coefficient replacement/combination portion for replacing and combining Nxc3x97N location data with Nxc3x97N wavelet coefficients selected among Mxc3x97M wavelet coefficients in accordance with a predetermined rule to then output the Nxc3x97N location data and replaced Mxc3x97M wavelet coefficients, a fist inverse discrete wavelet transform portion for performing inverse discrete wavelet transform on the replaced Mxc3x97M wavelet coefficients to generate a combined host image, a compression portion for compressing the combined host image and the Nxc3x97N location data, a decompression portion for receiving the bitstreams having the combined host image and the Nxc3x97N location data compressed therein, and decompressing the same to output the combined host image, and Nxc3x97N location data representing the locations of signature image discrete wavelet coefficients, a third discrete wavelet transform portion for performing discrete wavelet transform on the combined host image to obtain Mxc3x97M wavelet coefficients, a coefficient separating portion for separating the Nxc3x97N location data from the Mxc3x97M wavelet coefficients using Nxc3x97N wavelet coefficients, a second inverse discrete wavelet transform portion for performing inverse discrete wavelet transform on the Nxc3x97N wavelet coefficients to generate a restored signature image, a second original signature image storage portion for storing the signature image, which is suitable to the performance of an ANOVA technique and which is the same as that used in watermarking of the host image as the original signature image, and an ANOVA portion for applying the original signature image and the restored signature image to an ANOVA technique to output variance characteristic data of the restored signature image as image quality indication data.
According to still further another aspect of the present invention, there is provided a digital image coding method for recording a signature image on a host image using watermarking, including the steps of: (a) performing discrete wavelet transform on a host image to be transmitted, thereby obtaining Mxc3x97M discrete wavelet coefficients where M is a predetermined positive integer, (b) storing and supplying an image suitable to an ANOVA technique as an original signature image, (c) receiving the original signature image and performing discrete wavelet transform thereon, thereby obtaining Nxc3x97N discrete wavelet coefficients where N is a predetermined positive integer smaller than M, (d) discriminating Mxc3x97M discrete wavelet coefficients and selecting the Nxc3x97N replacing locations having high significance according to a predetermined rule, (e) replacing and combining the coefficients of the selected Nxc3x97N locations among Mxc3x97M discrete wavelet coefficients with Nxc3x97N wavelet coefficients, (f) performing inverse discrete wavelet transform on the replaced Mxc3x97M wavelet coefficients to generate a combined host image, and (g) compressing the combined host image and the Nxc3x97N location data.
According to yet another aspect of the present invention, there is provided a digital image decoding method for receiving bitstreams having a signature image recorded on a host image using watermarking, and restoring the signature image and the host image, including the steps of: (a) decompressing the received bitstreams, thereby obtaining a host image and Nxc3x97N location data, (b) performing discrete wavelet transform on the host image, thereby obtaining Mxc3x97M wavelet coefficients, (c) separating Nxc3x97N wavelet coefficients corresponding to Nxc3x97N location data, among Mxc3x97M wavelet coefficients, (d) performing inverse discrete wavelet transform on the Nxc3x97N wavelet coefficients, thereby restoring the signature image, (e) storing as the original signature image the signature image, which is suitable to the application of an ANOVA technique and which is the same as that used in watermarking of the host image during encoding, and (f) applying the original signature image and the restored signature image to an ANOVA technique to output variance characteristic data of the restored signature image as image quality indication data.
Finally, the invention comprises a program media having stored thereon a computer program embodying the foregoing methods.